fcitx is a im framework. https://code.google.com/p/fcitx/ The problem is with it's window, it window is using override-redirect, and its window will be show/hide with XMapWindow and XUnmapWindow frequently when using it.
I'm not a e17 user but upstream fcitx developer. Some fcitx users report that while using e17 with composite enabled, sometimes fcitx's window is not hide correctly. Since I have never notice similar problem with any other window manager so I suppose it's related to e17 and after them disable the composite this problem is resolved.
This problem is reproduced by at least three people under up-to-date Archlinux.
I can provide extra information or test if required.